Park Kwang Ho (Choi Jin Hyuk) is a police detective in the violent crimes unit who is tracking a dangerous serial killer in 1986. When his own daughter’s life in danger, he is determined to catch the dangerous killer before it’s too late. But when he chases the killer through a tunnel, Kwang Ho discovers that he has traveled in time to the present time of 2017, and the killer is still at large.

With so many changes to society and technology in 30 years, Kwang Ho is completely out of his element with his old-fashioned ways. But with the help of young police detective Kim Sun Jae (Yoon Hyun Min) and Shin Jae Yi (Lee Yoo Young), a criminal psychology professor, can Kwang Ho finally bring the serial killer to justice?